1. Field of the Invention
The present invention relates to an image blur correction apparatus for correcting image blurs generated by vibration etc. when capturing an image, a lens barrel having the image blur correction apparatus, an image capture apparatus provided with the lens barrel, such as a digital still camera, a video camera, etc.
2. Description of the Related Art
In recent years, there is a remarkable improvement in performance of image capture apparatuses, such as a digital still camera and a video camera, whereby anyone can easily capture a still image and a moving image of high definition and a high performance. Such an improvement in the performance of the image capture apparatus considerably relies on high performances of a lens, imaging devices (CCD, CMOS, etc.), and an image processing circuit.
However, even if the performances of the lens, the imaging device, etc. are improved, when a tremble or a shake arises to the hand supporting the camera (image capture apparatus), blurs may occur on a screen of high resolution, and an image with the blurs state may be captured. Therefore, in some relatively expensive cameras, an image blur correction apparatus which corrects the image blurs generated by camera shake at the time of capturing the image etc. is installed. However, originally, the camera correcting image blur is required rather for a popular model used by majority of people having little shooting experience, but not for a high class model used by a professional photographer.
Further, in general, there is a strong demand for a camera (image capture apparatus) to be reduced in size and weight, and a camera which is light and easy to carry is preferred. However, an image blur correction apparatus has been comparatively large in size. Therefore, if the related art image blur correction apparatus is installed in a camera body, size of camera as whole becomes large, and thus demand of the reduction in size and weight can not be met. Further, there has been an issue that a lot of components are needed for the related art image blur correction apparatus, and the cost increases as number of components increase.
As a related art image blur correction apparatus of this type, there are type of apparatus disclosed in Japanese Patent Application Publication No. JP H10-319465 (Patent Document 1), for example. Patent Document 1 discloses one that relates to a lens shifting apparatus for shifting a lens which causes an optical axis of a lens group etc. to be eccentric. The lens shifting apparatus disclosed in Patent Document 1 is characterized by including “a lens for causing an optical axis to be eccentric, a fixed member which has a reference plane perpendicular to the optical axis, a movable member having a plane which is parallel to and faces the reference plane, holding the lens, and shifting the lens within a plane perpendicular to the optical axis, at least three rotatable balls sandwiched between the two planes, a hold member for holding the balls, and an elastic member for generating a force to sandwich the balls between the two planes and preventing the movable member from rotating around the optical axis”.
According to the invention as described in Patent Document 1, the effect of “being able to shift the lens in a manner lenses are kept perpendicular to the optical axis without backlash while reducing drive resistance as much as possible with simple structure” (see paragraph [0060]) is expected.
The lens shifting apparatus as described in Patent Document 1 is provided with the movable member for holding the lens (hereafter referred to as “correction lens”, since it is equivalent to the correction lens in an embodiment of the present invention) for causing the optical axis to be eccentric, the fixed member for supporting the movable member in a movable manner, the rotatable balls interposed between the movable member and the fixed member. By detecting a position of the movable member (correction lens) by a position detector, the correction lens is driven and controlled to carry out the image blur correction. In order to detect the position of this movable member, it is necessary to set up the reference position of the movable member. Therefore, in the lens shifting apparatus as described above, the reference position of the movable member is typically set up by using a chart for adjustment.
Now, the setup of the reference position of the movable member using the chart will be described. In order to set up the reference position of the movable member, the lens shifting apparatus is first installed in a lens barrel provided with a lens group and an imaging device. Next, the chart for adjustment is arranged at front side of an object lens of the lens barrel whereto the lens shifting apparatus is installed, and an image of the chart is formed on the image capture side of the imaging device. By viewing the formed image of the chart, the movable member of the lens shifting apparatus is driven such that the optical axis of the correction lens are in alignment with the optical axis of the lens group of the lens barrel. Then, a position where both of the optical axes are aligned is set as the reference position of the movable member.
However, in the setup of the reference position of the movable member using the chart as described above, the lens shifting apparatus needs to be installed in the lens barrel, and there has been an issue that the reference position of the movable member can not be set up solely by the lens shifting apparatus. Further, it is necessary to prepare a device for displaying the image of the chart and large space for installing the chart. Furthermore, manpower for installing the chart increases, and thus there arise an issue that the costs are increased considerably.
Then, it is conceivable that the movable member is moved to the position in which the movement of the movable member is limited, or a so-called mechanism end (which means “end of mechanical chassis”), and based on output of the position detector at this time, the reference position of the movable member is set up. Now, the setup of the reference position of the movable member using the mechanism end will be described with reference to FIGS. 39 and 40.
FIG. 39 is a plan view of the image blur correction apparatus using a sphere as a guide of the movable member with respect to the fixed member. This image blur correction apparatus 300 includes a moving frame (movable member) 303 having a correction lens 304 in the central part, a support frame (fixed member) 302 which movably supports the moving frame 303 through a sphere 305 in a movable manner, a first electric actuator 306A which moves the correction lens 304 in the first direction X, a second electric actuator 306B which moves the correction lens 304 in the second direction Y, a first Hall device 307a which detects a position of the moving frame 303 (correction lens) with respect to the first direction X, a second Hall device 307b which similarly detects a position with respect to the second direction Y, etc.
The first electric actuator 306A is arranged on “−” side which is one side of the first direction X of the correction lens 304 disposed in the center of the image blur correction apparatus 300. The second electric actuator 306B is arranged on “−” side which is the other side of the second direction Y orthogonal to the first direction X of the correction lens 304 of the image blur correction apparatus 300. The first electric actuator 306A has a magnet 309a, a coil 310a, and an opposing yoke (not shown). Further, the second electric actuator 306B has a magnet 309b, a coil 310b, and an opposing yoke (not shown).
The magnet 309a of the first electric actuator 306A is fixed to “+” side of the first direction X of the moving frame 303, and the magnet 309b of the second electric actuator 306B is fixed to the other side (−) of the second direction Y of the moving frame 303. The coil 310a of the first electric actuator 306A is adapted to face the magnet 309a, the coil 310b of the second electric actuator 306B is adapted to face the magnet 309b, and these coils 310a and 310b are fixed to the support frame 302 via a flexible wiring board 311. Further, the opposing yokes of the first and second electric actuators 306A and 306B are attracted by magnetic force of the magnets 309a and 309b, and the moving frame 303 is urged towards side of the support frame 302 through the sphere 305.
The first Hall device 307a out of the two Hall devices which detect the position of the correction lens is arranged in the opening of the coil 310a, and adapted to face a boundary line (polar boundary) between N pole and S pole of the magnet 309a. Further, the second Hall device 307b is arranged in the opening of the coil 310b, and adapted to face a polar boundary of the magnet 309b. These first and second Hall devices 307a and 307b detect the magnetic force of N pole and S pole of two magnets 309a and 309b, and output the detection signals in response to strength of the magnetic force, respectively.
The moving frame 303 is provided with a limit hole 303a in an opposing position across the correction lens 304. This limit hole 303a is formed to be quadrangular, and has two sides extended in the first direction X and two sides extended in the second direction Y. Further, the support frame 302 is provided with a limit projection 302a to be inserted through the limit hole 303a of the moving frame 303. This limit projection 302a is in the shape of a square pole whose four side surfaces respectively face four sides of the limit hole 303a in a state where it is inserted into the limit hole 303a. A move limit mechanism for limiting a moving range of the moving frame 303 is configured by the limit projection 302a and limit hole 303a. 
Next, the setup of the reference position of the moving frame 303 using the mechanism end in the image blur correction apparatus 300 having such a structure as described above will be explained. The setup of the reference position of the moving frame 303 using the mechanism end is performed by setting up a reference position with respect to the first direction X of the moving frame 303, and a reference position with respect to the second direction Y.
First, the setup of the reference position with respect to the first direction X of the moving frame 303 will be described. In order to set up the reference position with respect to the first direction X of the moving frame 303, the moving frame 303 is adapted to move to “+” side of the first direction X, and the limit projection 302a is brought into abutment with the limit hole 303a, as shown in FIG. 40A. Output (hereafter referred to as “X-direction mechanism end “+” output”) of the first Hall device 307a at this time is detected.
Next, the moving frame 303 is moved to “−” side of the first direction X, and the limit projection 302a is brought into abutment with the limit hole 303a, as shown in FIG. 40B. Output (hereafter referred to as “X-direction mechanism end—output”) of the first Hall device 307a at this time is detected. Then, an output value which is intermediate of the X-direction mechanism end “+” output and the X-direction mechanism end “−” output is calculated, so that a position where the output is detected is set as the reference position with respect to the first direction X of the moving frame 303. Similarly, the setup of the reference position of the moving frame 303 is completed by setting up the reference position with respect to the second direction Y of the moving frame 303.
However, in the image blur correction apparatus 300, when the moving frame 303 is moved to the mechanism end on “+” side of the first direction X as shown in FIG. 41A, the moving frame 303 rotates around a fulcrum, which is one corner of the limit projection 302a. Similarly, when the moving frame 303 is adapted to move to the extent of the mechanism end on “−” side of the first direction X as shown in FIG. 41B, the moving frame 303 rotates around a fulcrum, which is one corner of the limit projection 302a. 
If the moving frame 303 rotates, a relative position of the first Hall device 307a and the magnet 309a is shifted to cause an error in the X-direction mechanism end “+” output and the X-direction mechanism end “−” output. Thus, an error arises also in a middle value obtained by computing both the X-direction mechanism end “+” output and the X-direction mechanism end “−” output, and the reference position of the moving frame 303 is set at an inappropriate position. As a result, an issue arises in that the moving frame 303 (correction lens 304) may not be driven or controlled exactly.
It should be noted that if either one of the error in the X-direction mechanism end “+” output or the error of the X-direction mechanism end “−” output is plus and the other is minus, and when absolute values are the same, no shift is caused in the reference position. However, even in such a case, an error arises in the X-direction mechanism end “+” output and the X-direction mechanism end “−” output to cause a difference between the position of the moving frame 303 detected from the output of the first Hall device 307a and the actual position of the moving frame 303. Therefore, it has not been possible to perform accurate drive and control of the moving frame 303 (correction lens 304).